The effect of recombinant Factor IX-FIAV in In-vitro thrombin generation in hemophilia A patient samples

Hemophilia A (HA) is a rare X-linked recessive hereditary bleeding disorder,
caused by factor VIII deficiency. Many severe (FVIII level <0.01 IU/ml)
hemophilia A patients undergo prophylactic treatment by three weekly infusions
of FVIII concentrate to prevent bleeding, especially in joints. Gene therapy
with FVIII is presently being developed which normalizes coagulation, reduce
bleeding complications and the need for prophylaxis, as shown in recent trials.
However, a gradual decrease of FVIII levels after gene therapy has been noted.
Taken together, these data support the notion that FVIII-mediated gene therapy
might be less than optimal, suggesting that novel approaches are needed.
Recently, FIX variants were described which comprise mutations in the FIX
protein and can catalyze interactions with FX in the absence of FVIII. One of
these FIX variants, FIX-FIAV, has four amino acid difference compared to
wildtype FIX. Gene therapy approaches are being developed using an AAV vector
to deliver a transgene that encodes for FIX-FIAV, AMT-180, representing a novel
avenue to treat hemophilia A patients. Such an approach has proven successful
in pre-clinical studies. Normal and hemophilia A mice show an increase in
circulating FIX-FIAV levels after gene therapy, and data support improved
clotting activity in the absence of FVIII. Safety assessments in these animals
demonstrated no elevation of coagulation activation markers, no signs of
thrombus formation and no other adverse events. Further, in silico and in vitro
assessments showed low immunogenicity risk. In vitro data also support efficacy
of this approach, but translational data are limited due to a shortage of HA
patient samples. If successful, novel FIX-FIAV gene therapy could be applied in
hemophilia A patients with and without inhibitory FVIII antibodies.

To obtain blood samples from twenty-one adult hemophilia A patients with and
without inhibiting FVIII antibodies for biochemical analyses in order to show
the efficacy and determine the potency of recombinant FIX-FIAV treatment using
thrombin generation and clotting activity tests in vitro. The blood samples
will be taken at trough levels of the respective treatment regime, for example
before the next planned dose of FVIII in case of prophylactic treatment.

Non-randomized, non-interventional, cross-sectional study

Only one venepuncture will be performed. Severe hemophilia A patients on
prophylactic treatment will be included but just before subsequent treatment
with FVIII.